54. While treating of education, it is not out of place to show here how an ecclesiastical writer, who flourished in more recent times, during the Renaissance, the holy and learned Cardinal Silvio Antoniano, to whom the cause of Christian education is greatly indebted, has set forth most clearly this well established point of Catholic doctrine. He had been a disciple of that wonderful educator of youth, St. Philip Neri; he was teacher and Latin secretary to St. Charles Borromeo, and it was at the latter's suggestion and under his inspiration that he wrote his splendid treatise on The Christian Education of Youth. In it he argues as follows:
The more closely the temporal power of a nation aligns itself with the spiritual, and the more it fosters and promotes the latter, by so much the more it contributes to the conservation of the commonwealth. For it is the aim of the ecclesiastical authority by the use of spiritual means, to form good Christians in accordance with its own particular end and object; and in doing this it helps at the same time to form good citizens, and prepares them to meet their obligations as members of a civil society. This follows of necessity because in the City of God, the Holy Roman Catholic Church, a good citizen and an upright man are absolutely one and the same thing. How grave therefore is the error of those who separate things so closely united, and who think that they can produce good citizens by ways and methods other than those which make for the formation of good Christians. For, let human prudence say what it likes and reason as it pleases, it is impossible to produce true temporal peace and tranquillity by things repugnant or opposed to the peace and happiness of eternity.
67. In this extremely delicate matter [of "sex-education"], if, all things considered, some private instruction is found necessary and opportune, from those who hold from God the commission to teach and who have the grace of state, every precaution must be taken. Such precautions are well known in traditional Christian education, and are adequately described by Antoniano cited above, when he says:
Such is our misery and inclination to sin, that often in the very things considered to be remedies against sin, we find occasions for and inducements to sin itself. Hence it is of the highest importance that a good father, while discussing with his son a matter so delicate, should be well on his guard and not descend to details, nor refer to the various ways in which this infernal hydra destroys with its poison so large a portion of the world; otherwise it may happen that instead of extinguishing this fire, he unwittingly stirs or kindles it in the simple and tender heart of the child. Speaking generally, during the period of childhood it suffices to employ those remedies which produce the double effect of opening the door to the virtue of purity and closing the door upon vice.
72. It is not our intention to treat formally the question of domestic education, nor even to touch upon its principal points. The subject is too vast. Besides there are not lacking special treatises on this topic by authors, both ancient and modern, well known for their solid Catholic doctrine. One which seems deserving of special mention is the golden treatise already referred to, of Antoniano, On the Christian Education of Youth, which St. Charles Borromeo ordered to be read in public to parents assembled in their churches.
Surprisingly, On the Christian Education of Youth is not available, neither in translation nor in the original Italian, neither in print nor electronically, as far as I know. Consequently, I have obtained and scanned a rare 1821 Milan, two-volume edition (WorldCat OCLC: 46769058), 843 pages in total, and have translated into English the first approximately 25 chapters, with Douay-Rheims for Biblical verses (300 kB PDF).